1. Field of the Invention
The present invention relates to a gas turbine output learning circuit and a combustion control device for a gas turbine having the gas turbine output learning circuit.
2. Description of the Related Art
A gas turbine including a gas turbine body, a combustor, a compressor having an inlet guide vane (IGV), and a fuel flow rate control valve controlling fuel supply to the fuel nozzle is provided with a combustion control device for the gas turbine configured to control the fuel supply to the fuel nozzle by controlling an aperture of the fuel flow rate control valve, an IGV control device configured to control an aperture of the IGV, and so forth.
In the meantime, although details will be described later, concerning the combustion control device for a gas turbine the inventors of this invention have disclosed a combustion control device for a gas turbine in non-published Japanese Patent Application No. 2005-266357. The combustion control device is capable of controlling a ratio of fuel such as a pilot ratio or a degree of aperture of a combustor bypass valve in response to a combustion gas temperature at an inlet of a gas turbine in conformity to an original concept by computing a combustion load command value (CLCSO) that is proportional to the combustion gas temperature at the inlet of the gas turbine. Moreover, the inventors have also disclosed a concept of providing the combustion control device for a gas turbine with a learning circuit for a gas turbine output in consideration of reduction in the gas turbine output (a power generator output) attributable to deterioration in a performance of the gas turbine such as deterioration in a compression performance of a compressor.
Although details will be described later, this gas turbine output learning circuit in non-published Japanese Patent Application No. 2005-266357 is configured to judge that the combustion gas temperature at the inlet of the gas turbine reaches the maximum combustion gas temperature (such as 1500° C.) based on an exhaust gas temperature of the gas turbine body and a pressure ratio of the compressor. Thereafter, the gas turbine output learning circuit compares the gas turbine output (the power generator output) corresponding to the maximum combustion gas temperature computed by gas turbine output computing means with a measured gas turbine output (a power generator output). Thereby, the gas turbine output learning circuit corrects the computed gas turbine output to match with the measured gas turbine output. In addition to non-published Japanese Patent Application No. 2005-266357, the prior art documents also include Japanese Patent Application Publication No. 2004-190632 and Japanese Patent Application Publication No. Hei 8 (1996)-246903.
However, the gas turbine output learning circuit disclosed in non-published Japanese Patent Application No. 2005-266357 is configured to start learning after the judgment that the combustion gas temperature at the inlet of the gas turbine reaches the maximum combustion gas temperature, that is, after the judgment that the gas turbine output reaches a rated output (a rated load). Accordingly, a trouble may be incurred by a command from a central load dispatching center, for example, in a case where the learning circuit is applied to a gas turbine which is configured to perform part-load operation frequently.
Specifically, in a case where the above-described gas turbine output learning circuit is applied to the combustion control device for the gas turbine which is often operated in a (part-load) state in which the combustion gas temperature at the inlet of the gas turbine is adjusted to a lower temperature than the maximum combustion gas temperature without raising the combustion gas temperature up to the maximum combustion gas temperature, there is a risk that correction of temperature controlled MW will not take place as the learning is never started. Since this temperature controlled MW is used for computation of the CLCSO, if the temperature controlled MW is not corrected in spite of reduction in the gas turbine output (the power generator output) attributable to deterioration in the performance of the gas turbine, the CLCSO may be deviated from the actual combustion gas temperature at the inlet of the gas turbine. In a case where the combustion control is performed based on this CLCSO, there is a risk of causing combustion vibration.